<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		.box {
			width: 300px;
			height: 300px;
			border: 1px solid red;
			margin: 50px auto;
			/* 径向渐变 */
			background-image: radial-gradient(
				 100px at center,
				 red,
				 blue
			);
		}
	</style>
</head>
<body>
	<div class="box"></div>
</body>
</html>